Silicon photonic switch enabling up to 2500 switch elements to be presented at OFC 2015

March 11, 2015
The photonic switch is the largest-scale and lowest-energy-loss such switch reported to date.

Researchers at the University of California, Berkeley have developed a novel silicon photonic switch that is the largest-scale and lowest-energy-loss such switch reported to date. It features a submicrosecond switching time and a broad bandwidth of hundreds of nanometers; uses will include communications between servers at datacenters with rates exceeding 100 Gbit/s.

The researchers will present their photonic switching innovation on 23 March 2015 during the Optical Fiber Communication Conference and Exposition (OFC) in Los Angeles, California, USA. A step forward towards achieving large-scale silicon photonic switches for high-traffic datacenter networks, the new device will boost other technologies that rely on manipulating multichannel optical signals, such as secure communications and quantum computing.

"Our photonic switch has 50 input and 50 output channels, for a total of 2500 switching elements located on the cross points of these channels, which is the largest-scale silicon photonic switch ever reported," says Tae Joon Seok, a postdoctoral researcher at the Integrated Photonics Laboratory at the university. "The switch can be compactly integrated on a silicon chip smaller than 1 cm x 1 cm."

Seok notes that the largest-scale silicon photonic switch previously reported by other groups has 8 input and 8 output channels.

Conventional silicon photonic switches consist of a number of smaller optical switches with one or two input and output channels (1x2 or 2x2) as switch elements. These elements are cascaded with each other to form a two-dimensional switching network. When optical signals are transmitted in the network, the light undergoes energy losses accumulated as it goes through multiple switching elements, and because these switching elements cannot transfer 100% of light energy, the size of switches are limited as a result.

Fast MEMS switching
To address this problem, Seok and his co-workers designed a new switch architecture that enables scalability. Rather than connecting smaller optical switches in succession to form a switching network, the new architecture is a single-stage switch with a MEMS switching mechanism, which eliminates the problem of cumulative loss.

According to Seok, he and his colleagues first patterned a bottom silicon layer to create the east-to-west input and north-to-south output channels. Then, with the aid of a sacrificial spacer layer, a top silicon layer was built on and patterned to form a specific type of switching element -- an adiabatic coupler, which is a gradually tapered waveguide that transfers light from one channel to another channel without wavelength dependency.

Seok says the novel switch architecture is highly scalable, possibly allowing switches larger than 100x100 ports fabricated on a tiny chip. The newly designed switch has a bandwidth about 10 times broader than that of regular silicon switches and provides larger capacity for the network to process information.

"Although commercially available [devices] like 3D-MEMS optical switches can also have up to hundreds of input/output ports and low energy loss, the switch speed is slow, around millisecond level, and the physical size is large," Seok said.

"Our switch features sub-microsecond switching time, which is three orders of magnitude faster than 3D-MEMS switches. Also, the new switch is based on silicon photonics and can be implemented on a tiny silicon chip less than 1 cm x 1 cm, which may reduce the manufacturing costs and enable a low-cost mass production."

About the presentation
The presentation, "50x50 Digital Silicon Photonic Switches with MEM-Actuated Adiabatic Couplers," by Tae Joon Seok, Niels Quack, Sangyoon Han, Ming C. Wu, will take place at 14:30, Monday, 23 March 2015, in Room 403A at the Los Angeles Convention Center, Los Angeles, California, USA.

OFC is managed by The Optical Society (OSA) and co-sponsored by OSA, the IEEE Communications Society (IEEE/ComSoc), and the IEEE Photonics Society. OFC 2015 takes place 22-26 March at the Los Angeles Convention Center in Los Angeles, California, USA.

For more information on OFC, visit

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